Abstract: A waveguide 10 is located beside a phase mask 12, which is driven, with a ramp waveform, to undergo oscillating motion along its longitudinal axis. The phase mask 12 is illuminated with a CW UV laser beam 16, thereby generating a UV interference fringe pattern extending across the waveguide 10. The waveguide 10 moves continuously in one direction along its longitudinal axis, past the phase mask 12. Each period of the ramp waveform comprises two parts: the first part causes the phase mask 12 to move, in the same direction and at the same speed as the waveguide 10, for a distance equal to the width of the fringe pattern. As a result, the UV interference fringe pattern moves along with the waveguide 10, and a section of grating is fabricated. The second part causes the phase mask 12 to move rapidly in the opposite direction, flying back to its starting position and the next section of the grating is fabricated.